Cold starting an engine at lower ambient temperatures may be improved by enriching an air-fuel mixture supplied to an engine cylinder. Increasing the amount of fuel injected to a cylinder can increase an amount of fuel that vaporizes in the cylinder so that the air-fuel mixture in the cylinder may be ignited. However, the additional fuel may also cause soot or conductive deposits including liquid fuel to form on the ceramic of the center electrode at a spark plug in the cylinder, thereby shunting the spark gap and reducing the possibility of creating a spark within the cylinder. Therefore, it may be desirable to determine whether or not soot is forming on a spark plug.
One way to ascertain whether or not soot is forming on a spark plug is to monitor engine operation for misfires. Engine misfires may be determined from changes in engine speed. However, engine emissions can degrade in the presence of engine misfires. For example, engine hydrocarbon emissions can increase due to engine misfires. Consequently, determining whether or not spark plugs are laden with soot via detected engine misfires is not as desirable as detecting spark plug soot without the engine having to misfire.
The inventors herein have recognized the above-mentioned disadvantages and have developed a system for monitoring a spark plug, comprising: an ignition coil including primary and secondary coils; a spark plug in electrical communication with the secondary coil; a sense resistor electrically coupled in series with the secondary coil and spark plug; and a controller including instructions stored in non-transitory memory to adjust operation of an engine responsive to an electrical characteristic of the sense resistor during an ignition dwell period.
By monitoring voltage or current of a sense resistor during an ignition dwell period, it may be possible to determine an amount of carbonaceous soot or other conductive deposits that may be present on the center electrode ceramic of a spark plug. Further, soot accumulation may be determined before engine misfire occurs because the voltage across the sense resistor is indicative of even small amounts of accumulated soot. Therefore, soot accumulation may be determined before an engine misfire occurs. In one example, a voltage across a sense resistor is driven more negative during an ignition dwell period as an amount of carbonaceous soot deposited to a spark plug center electrode ceramic increases. The system attempts to remove the carbonaceous soot from the spark plug electrode by increasing temperature and pressure in the cylinder in which the spark plug supplies spark.
The present description may provide several advantages. In particular, the approach detects carbonaceous soot deposits in a way that does not require an engine misfire to occur. Thus, the approach may improve engine emissions by taking actions to remove carbonaceous soot from a spark plug before engine misfire is detected. In addition, provides an indication of spark duration so that engine misfires may be determined. Further, by removing soot before a misfire caused by soot occurs, engine emissions may be reduced.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.